BACKGROUND: Fine woody debris (FWD; deadwood < 10 cm diameter) is a crucial but often overlooked component of forest ecosystems. It provides habitat for microbial communities and enhances soil fertility through nutrient cycling. This role is especially important in managed forests, which typically have limited deadwood stocks. Climate change is increasing forest disturbances and expanding early successional forests with low canopy cover, yet the effects on microbial communities and related processes remain poorly understood. RESULTS: In a ten-year canopy manipulation experiment, we examined the decomposition of FWD of Fagus sylvatica and Abies alba. Increased canopy openness significantly decreased bacterial diversity in decomposing FWD and altered the community composition in surrounding soil. Decomposition time was the main factor shaping bacterial community structure in FWD, with tree species and canopy cover also contributing. We identified bacterial groups involved in carbohydrate degradation, fungal biomass breakdown, and nitrogen fixation. Importantly, bacterial communities in fully decomposed FWD remained distinct from soil communities. CONCLUSIONS: Deadwood decomposition and nutrient cycling are driven by complex ecological interactions. Microbial community dynamics are influenced by the interplay of FWD decomposition stage, tree species, and microclimatic conditions. Bacterial communities, although less frequently studied in this context, appear more stable over time than previously studied fungi. This stability may help sustain decomposition processes and nutrient turnover under the environmental variability associated with global change.

Animal Ecology Faculty of Biology Philipps Universität Marburg 35043 Marburg Germany

Bavarian Forest National Park Freyunger Straße 2 94481 Grafenau Germany

Chair Ecology of Fungi Bayreuth Center of Ecology and Environmental Research University of Bayreuth Universitätsstraße 30 95440 Bayreuth Germany

Chair of Conservation Biology and Forest Ecology Biocenter Julius Maximilians Universität Würzburg 96181 Rauhenebrach Germany

Institute of Soil Biology and Biogeochemistry Biology Centre of the Czech Academy of Sciences Na Sádkách 7 37005 České Budějovice Czech Republic

Laboratory of Environmental Microbiology Institute of Microbiology of the Czech Academy of Sciences Vídeňská 1083 14200 Praha 4 Czech Republic

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